Work Function Tailoring for Nonvolatile Memory Applications

ABSTRACT

Embodiments of the invention generally relate to a resistive switching nonvolatile memory device having an interface layer structure disposed between at least one of the electrodes and a variable resistance layer formed in the nonvolatile memory device, and a method of forming the same. Typically, resistive switching memory elements may be formed as part of a high-capacity nonvolatile memory integrated circuit, which can be used in various electronic devices, such as digital cameras, mobile telephones, handheld computers, and music players. In one configuration of the resistive switching nonvolatile memory device, the interface layer structure comprises a passivation region, an interface coupling region, and/or a variable resistance layer interface region that are configured to adjust the nonvolatile memory device&#39;s performance, such as lowering the formed device&#39;s switching currents and reducing the device&#39;s forming voltage, and reducing the performance variation from one formed device to another.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional claiming priority to U.S. patentapplication Ser. No. 13/156,624, filed 9 Jun. 2011, which is entirelyincorporated by reference herein for all purposes.

BACKGROUND

This invention relates to nonvolatile memory elements, and moreparticularly, to methods for forming resistive switching memory elementsused in nonvolatile memory devices.

Nonvolatile memory elements are used in systems in which persistentstorage is required. For example, digital cameras use nonvolatile memorycards to store images and digital music players use nonvolatile memoryto store audio data. Nonvolatile memory is also used to persistentlystore data in computer environments.

Nonvolatile memory is often formed using electrically-erasableprogrammable read only memory (EPROM) technology. This type ofnonvolatile memory contains floating gate transistors that can beselectively programmed or erased by application of suitable voltages totheir terminals.

As fabrication techniques improve, it is becoming possible to fabricatenonvolatile memory elements with increasingly smaller dimensions.However, as device dimensions shrink, scaling issues are posingchallenges for traditional nonvolatile memory technology. This has ledto the investigation of alternative nonvolatile memory technologies,including resistive switching nonvolatile memory.

Resistive switching nonvolatile memory is formed using memory elementsthat have two or more stable states with different resistances. Bistablememory has two stable states. A bistable memory element can be placed ina high resistance state or a low resistance state by application ofsuitable voltages or currents. Voltage pulses are typically used toswitch the memory element from one resistance state to the other.Nondestructive read operations can be performed to ascertain the valueof a data bit that is stored in a memory cell.

Resistive switching based on transition metal oxide switching elementsformed of metal oxide (MO) films has been demonstrated. Although metaloxide (MO) films such as these exhibit bistability, the resistance ofthese films and/or the ratio of the high-to-low resistance states is(are) often insufficient to be of use within a practical nonvolatilememory device. For instance, the resistance states of the metal oxidefilm should preferably be significant as compared to that of the system(e.g., the memory device and associated circuitry) so that any change inthe resistance state change is perceptible. Since the variation in thedifference between the high and low resistive states is related to theresistance of the resistive switching layer, it is often hard to use alow resistance metal oxide film to form a reliable nonvolatile memorydevice. For example, in a nonvolatile memory that has conductive linesformed of a relatively high resistance metal such as tungsten, theresistance of the conductive lines may overwhelm the resistance of themetal oxide resistive switching element. This may make it difficult orimpossible to sense the state of the bistable metal oxide resistiveswitching element. Similar issues can arise from integration of theresistive switching memory element with current steering elements, suchas diodes and/or resistors. The resistance of the resistive switchingmemory element (at least in its high resistance state) is preferablysignificant compared to the resistance of the current steering elements,so that the unvarying resistance of the current steering element doesnot dominate the resistance of the switching memory element, and thusreduce the measurable difference between the “on” and “off” states ofthe formed memory device (i.e., logic states of the device). However,since the power that can be delivered to a circuit containing a seriesof resistive switching memory elements and current steering elements istypically limited in most conventional nonvolatile memory devices (e.g.,CMOS driven devices), it is desirable to form each of the resistiveswitching memory elements and current steering elements in the circuitso that the voltage drop across each of these elements is small, andthus resistance of the series connected elements does not cause thecurrent to decrease to an undesirable level due to the fixed appliedvoltage (e.g., ˜2-5 volts).

As nonvolatile memory device sizes shrink, it is important to reduce therequired currents and voltages that are necessary to reliably set, resetand/or determine the desired “on” and “off” states of the device tominimize resistive heating of the device and cross-talk between adjacentdevices. Moreover, in cases where multiple formed memory devices areinterconnected to each other and to other circuit elements it isdesirable to minimize the device performance variation between onedevice to the next to assure that the performance of the formed circuitperforms in a desirable manner.

Therefore, it is desirable to form a nonvolatile memory device that hasa low operating current and reduced device performance variability.

SUMMARY

Embodiments generally relate to a resistive switching nonvolatile memorydevice having an interface layer structure disposed between at least oneof the electrodes and a variable resistance layer formed in thenonvolatile memory device. The resistive switching memory elements maybe formed as part of a high-capacity nonvolatile memory integratedcircuit, which can be used in various electronic devices, such asdigital cameras, mobile telephones, handheld computers, and musicplayers. The resistive switching nonvolatile memory device, comprises apassivation region, an interface coupling region, and/or a variableresistance layer interface region that are configured to adjust thenonvolatile memory device's performance, such as lowering the formeddevice's switching currents and reducing the device's forming voltage,and reducing the performance variation from one formed device toanother.

Some embodiments may provide a nonvolatile memory element, comprising afirst electrode layer, a second electrode layer, a variable resistancelayer disposed between the first electrode layer and the secondelectrode layer, and a first interface layer disposed between the firstelectrode layer and the variable resistance layer, wherein the firstinterface layer comprises, a first passivation region disposed adjacentto the first electrode, and a first variable resistance interface regiondisposed adjacent to the variable resistance layer. In one example, thefirst electrode layer comprises a first material selected from a groupconsisting of titanium, aluminum, tungsten, tantalum, cobalt,molybdenum, nickel, vanadium, copper, platinum, palladium, iridium andruthenium, and the first passivation region comprises the first materialfound in the first electrode layer and a second material selected from agroup consisting of titanium, aluminum, tungsten, tantalum, cobalt,molybdenum, nickel, vanadium, copper, platinum, palladium, iridium, andruthenium, wherein the first material and the second material aredifferent materials.

Embodiments may further provide a nonvolatile memory element, comprisinga first electrode layer, a second electrode layer, a variable resistancelayer disposed between the first electrode layer and the secondelectrode layer, a first interface layer disposed between the firstelectrode layer and the variable resistance layer, wherein the firstinterface layer comprises a first passivation region disposed adjacentto the first electrode layer, and a first variable resistance interfaceregion disposed adjacent to the variable resistance layer, and a secondinterface layer disposed between the second electrode layer and thevariable resistance layer, wherein the second interface layer comprisesa second passivation region disposed adjacent to the second electrodelayer, and a second variable resistance interface region disposedadjacent to the variable resistance layer.

Embodiments may further provide a method of forming a nonvolatile memoryelement, comprising forming a first electrode layer comprising a firstelectrode material over a surface of a substrate, forming a firstinterface layer comprising a first interface material, wherein the firstinterface layer is in contact with the first electrode layer, forming asecond interface layer comprising a second interface material, forming avariable resistance layer comprising a variable resistance material,wherein the second interface layer is in contact with variableresistance layer and is disposed between the first interface layer andthe variable resistance layer, and heating the substrate to (a) form afirst interface region that comprises the first interface material andthe first electrode material, wherein the material in the firstinterface region has a work function greater than the work function ofthe first electrode material, and (b) form a second interface regionthat comprises the second interface material and the variable resistancematerial.

Embodiments may further provide a method of forming a nonvolatile memoryelement, comprising forming a first electrode layer comprising a firstelectrode material over a surface of a substrate, forming a firstinterface layer comprising a first interface material, wherein the firstinterface layer is in contact with the first electrode layer, forming asecond interface layer comprising a second interface material, forming avariable resistance layer comprising a variable resistance material,wherein the variable resistance layer is in contact with the secondinterface layer, and heating the substrate to a temperature betweenabout 550° C. and about 1000° C. for a period of time between about 30seconds and about 20 minutes at least once to form a first interfaceregion that comprises the first interface material and the firstelectrode material, wherein the material in the first interface regionhas a work function greater than the work function of the firstelectrode material, and form a second interface region that comprisesthe second interface material and the variable resistance material.

Embodiments may further provide a nonvolatile memory element, comprisinga first electrode layer comprising a first electrode material, a secondelectrode layer comprising a second electrode material, a variableresistance layer comprising a variable resistance material disposedbetween the first electrode layer and the second electrode layer, and afirst interface layer disposed between the first electrode layer and thevariable resistance layer, and comprising a first dielectric materialthat has a band gap greater than the band gap of the variable resistancematerial.

Embodiments may further provide a nonvolatile memory element, comprisinga first electrode layer, a second electrode layer, a variable resistancelayer comprising a variable resistance material disposed between thefirst electrode layer and the second electrode layer, a first interfacelayer disposed between the first electrode layer and the variableresistance layer, and comprising a first dielectric material that has aband gap greater than the band gap of the variable resistance material,and a second interface layer disposed between the second electrode layerand the variable resistance layer, and comprising a second dielectricmaterial that has a band gap greater than the band gap of the variableresistance material.

Embodiments may further provide a method of forming a nonvolatile memoryelement, comprising forming a first electrode layer comprising a firstelectrode material over a surface of a substrate, forming a firstinterface layer comprising a first interface material, wherein the firstinterface layer is in contact with the first electrode layer, forming asecond interface layer comprising a second interface material over thefirst interface layer, forming a third interface layer comprising athird interface material over the second interface layer, forming avariable resistance layer comprising a variable resistance material,wherein the third interface layer is in contact with the variableresistance layer, and the first, second or third interface materialshave a band gap that is larger than the band gap of the variableresistance material, and heating the substrate to (a) form a firstinterface region that comprises the first interface material and thefirst electrode material, wherein the material in the first interfaceregion has a work function greater than the work function of the firstelectrode material, and (b) form a second interface region thatcomprises the second interface material and the variable resistancematerial.

Embodiments may further provide a method of forming a nonvolatile memoryelement, comprising forming a first electrode layer comprising a firstelectrode material over a surface of a substrate, forming a firstinterface layer comprising a first interface material, wherein the firstinterface layer is in contact with the first electrode layer, forming asecond interface layer comprising a second interface material, forming athird interface layer comprising a third interface material, forming avariable resistance layer comprising a variable resistance material,wherein the third interface layer is in contact with the variableresistance layer, and the second interface material has a band gap thatis larger than the band gap of the variable resistance material, andheating the substrate to a temperature greater than about 550° C. andabout 1000° C. for a period of time between about 30 seconds and about20 minutes at least once to form a first interface region that comprisesthe first interface material and the first electrode material, whereinthe material in the first interface region has a work function greaterthan the work function of the first electrode material, and form asecond interface region that comprises the second interface material andthe variable resistance material.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description maybe had by reference to embodiments, some of which are illustrated in theappended drawings. It is to be noted, however, that the appendeddrawings illustrate only typical embodiments of this invention and aretherefore not to be considered limiting of its scope, for the inventionmay admit to other equally effective embodiments.

FIG. 1 illustrates an array of resistive switching memory elements inaccordance with an embodiment of the invention.

FIG. 2A is schematic representation of a memory device in accordancewith an embodiment of the invention.

FIG. 2B is schematic representation of a memory device having a diodetype current steering element in accordance with an embodiment of theinvention.

FIG. 2C is schematic representation of an array of memory devices inaccordance with an embodiment of the invention.

FIG. 2D is a graph illustrating the current (I) versus voltage (V)characteristics of a bipolar switching type memory element in accordancewith an embodiment of the invention.

FIGS. 3A-3C are schematic side cross-sectional views of a nonvolatilememory device in accordance with an embodiment of the invention.

FIG. 4A is a schematic side cross-sectional view of a memory elementdisposed in a nonvolatile memory device in accordance with an embodimentof the invention.

FIGS. 4B-4C are schematic side cross-sectional views of various stagesof the formation of a memory element in accordance with an embodiment ofthe invention.

FIG. 5 is a schematic side cross-sectional view of a memory elementdisposed in a nonvolatile memory device in accordance with an embodimentof the invention.

FIG. 6A is a schematic view of a band diagram taken at an electrodeinterface formed in a memory element in accordance with an embodiment ofthe invention.

FIG. 6B is a schematic view of a band diagram taken at an electrodeinterface that has an interface coupling region formed therein inaccordance with an embodiment of the invention.

FIG. 6C is a schematic view of a band diagram taken across a memoryelement in accordance with an embodiment of the invention.

FIG. 7 is a schematic depiction of a process for forming the switchingmemory device according to one embodiment of the invention.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

DETAILED DESCRIPTION

Embodiments of the invention generally relate to a resistive switchingnonvolatile memory device having an interface layer structure disposedbetween at least one of the electrodes and a variable resistance layerformed in the nonvolatile memory device, and a method of forming thesame. Typically, resistive switching memory elements may be formed aspart of a high-capacity nonvolatile memory integrated circuit, which canbe used in various electronic devices, such as digital cameras, mobiletelephones, handheld computers, and music players. In one configurationof the resistive switching nonvolatile memory device, the interfacelayer structure comprises a passivation region, an interface couplingregion, and/or a variable resistance layer interface region that areconfigured to adjust the nonvolatile memory device's performance, suchas lowering the formed device's switching currents and reducing thedevice's forming voltage, and reducing the performance variation fromone formed device to another. The use of resistive switching memoryelements to form memory arrays is merely illustrative, and one skilledin the art will appreciate that the formed devices may be used in otherdevice applications without deviating from the basic scope of theinvention described herein.

An illustrative memory array 100 of nonvolatile resistive switchingmemory devices 200, which each generally include at least one switchingmemory element 112, is illustrated in FIG. 1. Memory array 100 may bepart of a larger memory device or other integrated circuit structure,such as a system on a chip type device. Read and write circuitry isconnected to switching memory devices 200 using electrodes 102 andorthogonal electrodes 118. Electrodes, such as electrodes 102 andelectrodes 118, are sometimes referred to as word lines and bit lines,and are used to read and write data into the memory elements 112 in theswitching memory devices 200. Individual switching memory devices 200 orgroups of switching memory devices 200 can be addressed usingappropriate sets of electrodes 102 and 118. The memory elements 112 inthe switching memory devices 200 may be formed from one or more layers114 of materials, as indicated schematically in FIG. 1. In addition,memory arrays such as memory array 100 can be stacked in a verticalfashion to make multilayer memory array structures.

FIG. 2A schematically illustrates one example of a switching memorydevice 200 that contains a memory element 112, and an optional currentsteering device 216, which are disposed between the electrodes 102 and118. In one configuration, the current steering device 216 is anintervening electrical component, such as a p-n junction diode, p-i-ndiode, transistor, or other similar device that is disposed betweenelectrode 102 and memory element 112, or between the electrode 118 andmemory element 112. In one example, the current steering device 216 mayinclude two or more layers of semiconductor material, such as two ormore doped silicon layers, that are configured to allow or inhibit thecurrent flow in different directions through the memory element 112.

FIG. 2B schematically illustrates a switching memory device 200 thatcontains a memory element 112 and a diode type current steering device216 that preferentially allows current to flow through the memory device200 in a forward direction (“I⁺”). However, due to the design of thecurrent steering device 216, a reduced current can also flow in theopposing direction through the device by the application of a reversebias to the electrodes 102 and 118.

FIG. 2C schematically illustrates a series array of switching memorydevices 200A-200C that may be connected together to form part of ahigh-capacity nonvolatile memory integrated circuit. As illustrated inFIG. 2C, each of the switching memory devices 200A-200C may be connectedinternally in a formed chip package, or externally from a formed chippackage, by use of the electrodes 102A-102C and 118A-118C.

During operation, such as a read operation, the state of a memoryelement 112 in the switching memory device 200 can be sensed by applyinga sensing voltage (i.e., a “read” voltage V_(READ) (FIG. 2D)), such asapplying about +0.5 volts (V), to an appropriate set of electrodes 102and 118. Depending on its history, a memory element that is addressed inthis way may be in either a high resistance state (HRS) or a lowresistance state (LRS). The resistance of the memory element 112therefore determines what digital data is being stored by the memoryelement 112. If the memory element 112 is in the high resistance state,for example, the memory element may be said to contain a logic one(i.e., a “1” bit). If, on the other hand, the memory element is in thelow resistance state, the memory element may be said to contain a logiczero (i.e., a “0” bit). During a write operation, the state of a memoryelement can be changed by application of suitable write signals to anappropriate set of electrodes 102 and 118.

In some embodiments, the memory element 112 uses bipolar switching whereopposite polarity set and reset voltages are used to alter theresistance of the memory element between high and low resistance states.FIG. 2D schematically illustrates a log-log plot of current (I) versusvoltage (V) (e.g., reference numeral 251) of one example of a bipolarswitching curve 252 of a resistive switching type of memory element, andthus illustrates typical threshold values used to set and reset thecontents of a memory element 112. In one example, initially, memoryelement 112 may be in a high resistance state (e.g., storing a logic“zero”). The high resistance state of memory element 112 can be sensedby read and write circuitry 150 (FIG. 2A) using electrodes 102 and 118.For example, read and write circuitry may apply a read voltage V_(READ)to memory element 112, and can sense the resulting “off” current(I_(OFF)) that flows through memory element 112. When it is desired tostore a logic “one” in memory element 112, memory element 112 can beplaced into its low-resistance state. This may be accomplished by usingread and write circuitry 150 to apply a set voltage V_(SET) (e.g., −2 Vto −4 V) across electrodes 102 and 118. In one configuration, applying anegative V_(SET) voltage to memory element 112 causes memory element 112to switch to its low resistance state. In this region, the memoryelement 112 is changed so that, following removal of the set voltageV_(SET), memory element 112 is characterized by a low resistance state.It is believed that the change in the resistive state of the memoryelement 112 may be due to the redistribution or filling of traps (i.e.,“trap-mediated”), or defects, in the resistive switching layer (e.g.,variable resistance layer 206 (FIG. 3A)) when the device is reversebiased. The defects or traps, which are commonly formed during thedeposition and/or post-processing of the variable resistance layer 206,are often created by a non-stoichiometric material composition found inthe formed variable resistance layer 206. V_(SET) and V_(RESET) aregenerally referred to as “switching voltages” herein.

The low resistance state of the memory element 112 can be sensed usingthe read and write circuitry 150. When a read voltage V_(READ) isapplied to resistive switching memory element 112, the read and writecircuitry 150 will sense the relatively high “on” current value(I_(ON)), indicating that memory element 112 is in its low resistancestate. When it is desired to store a logic zero in memory element 112,the memory element can once again be placed in its high resistance stateby applying a positive reset voltage V_(RESET) (e.g., +2 V to +5 V) tomemory element 112. When read and write circuitry applies V_(RESET) tomemory element 112, memory element 112 enters its high resistance state.When the reset voltage V_(RESET) is removed from memory element 112,memory element 112 will once again be characterized by high resistancewhen the read voltage V_(READ) is applied. Voltage pulses can be used inthe programming of the memory element 112. For example, a 1 ms to 1 nssquare or trapezoidal shaped pulse can be used to switch the memoryelement 112. In some embodiments, it may be desirable to adjust thelength of the pulse depending on the amount of time needed to switch thememory element 112. By use of one or more of the embodiments describedherein, it has been found that the shape and length of the pulserequired to program the memory element 112 can be drastically reduced,thus improving the speed with which the memory element 112 can switchlogic states. In one example, a more conventionally configured memoryelement, which does not contain an interface layer structure may requirea trapezoidal pulse that had a rise time and fall time of about 40 nsand “on” period of about 500 ns to reliably program the memory element112, while a memory element having an interface layer structure, asdiscussed below, only requires a trapezoidal pulse that had a rise timeand fall time of about 10 ns and “on” period of about 50 ns. While thediscussion of the memory element 112 herein primarily provides bipolarswitching examples, some embodiments of the memory elements 112 may useunipolar switching, where the set and reset voltages have the samepolarity, without deviating from the scope of the invention describedherein.

In an effort to prepare the memory element 112 for use, it is common toapply a forming voltage (V_(FORM)) at least once across the electrodes102, 118 to “burn-in” the device, as briefly discussed above. It isbelieved that the application of a forming voltage, which is typicallysignificantly greater than the V_(RESET) and V_(SET) voltages, causesthe defects that are formed within the variable resistance layer 206during the device fabrication process to move, align and/or collectwithin various regions of the layer, causing the VR layer 206 toconsistently and reliably switch between the “on” and “off” resistivestates throughout the memory element's life. In one configuration, theforming voltage is between about 1 and about 5 times greater than theV_(RESET) or V_(SET) voltage. In one example, the forming voltage isbetween about 1.4 and about 2.5 times greater than the V_(RESET) orV_(SET) voltage. In one example, the forming voltage is between about 3and about 7 volts. However, it is noted that in some cases it isdesirable to form the memory element 112 so that the application of aforming voltage is not required at all to assure that the device willperform as desired throughout its life.

FIGS. 3A-3C are each schematic side cross-sectional views of a switchingmemory device 200, such as switching memory devices 200D-200F, that areformed from a series of deposited layers. In one example, as shown inFIGS. 3A-3C the integrated series of layers used to form a switchingmemory device 200 are formed over, or integrated with and distributedover, portions of a surface of a substrate 201 (e.g., silicon substrate,SOI substrate). In one embodiment, the switching memory device 200comprises a memory element 112 disposed between an electrode 102 and anelectrode 118. In another embodiment, as shown in FIGS. 3A-3C, theswitching memory devices 200D-200F each comprise an electrode 102, amemory element 112, optional intermediate electrode 210, an optionalcurrent steering device 216 and an electrode 118. It should be notedthat, in some configurations, the switching memory device 200 does notcontain a current steering device 216. Further, the electrode 118 andthe intermediate electrode 210 may both be the same element, or in somecases parts of a larger multilayered electrode element.

Generally, the memory element 112 comprises a variable resistance layer206 and one or more interface structures, such as a first interfacestructure 204 and/or a second interface structure 208, which aredisposed between the variable resistance layer 206 and an electrodedisposed in the switching memory device 200. In one embodiment of aswitching memory device, as shown in FIG. 3A, the memory elements 112comprises a first interface structure 204, a variable resistance layer206 and a second interface structure 208, wherein the first interfacestructure 204 is in contact with the electrode 102 and the variableresistance layer 206, and the second interface structure 208 is incontact with the intermediate electrode 210 and the variable resistancelayer 206. In another embodiment of a switching memory device, as shownin FIG. 3B, the memory elements 112 comprises a first interfacestructure 204 and a variable resistance layer 206, wherein the firstinterface structure 204 is in contact with the electrode 102 and thevariable resistance layer 206, and the intermediate electrode 210 is incontact with the variable resistance layer 206. In yet anotherembodiment of a switching memory device, as shown in FIG. 3C, the memoryelement 112 comprises a second interface structure 208 and a variableresistance layer 206, wherein the second interface structure 208 is incontact with the intermediate electrode 210 and the variable resistancelayer 206, and the electrode 102 is in contact with the variableresistance layer 206.

The variable resistance layer 206 can be a dielectric material, such asa metal oxide material or other similar material that can be switchedbetween at least two or more stable resistive states. In someembodiments, the variable resistance layer 206 is a high bandgapmaterial (e.g., bandgap >4 electron volts (eVs)), such as hafnium oxide(Hf_(x)O_(y)), tantalum oxide (Ta_(x)O_(y), aluminum oxide (Al_(x)O_(y),lanthanum oxide (La_(x)O_(y)), yttrium oxide (Y_(x)O_(y)), dysprosiumoxide (Dy_(x)O_(y)), ytterbium oxide (Yb_(x)O_(y)) and zirconium oxide(Zr_(x)O_(y)). It has been found that using high band gap variableresistance layer materials will improve data retention in the memoryelement 112, and reduce the leakage current in the formed memory elementdevice, since the amount of trapped charge in the variable resistancelayer material with a high band gap will be less than the amount oftrapped charge in the variable resistance layer material with a lowerband gap material, and the high band gap materials create a largebarrier height that the carriers have to cross during the read, set andreset operations. In other embodiments, lower bandgap metal oxidematerials can be used, such as titanium oxide (TiO_(x)), nickel oxide(NiO)_(x) or cerium oxide (CeO_(x)) may be advantageous for someembodiments. In some cases, a semiconductive metal oxide (p-type orn-type) such as zinc oxides (Zn_(x)O_(y)), copper oxides (Cu_(x)O_(y)),and their nonstoichiometric and doped variants can be used. The variableresistance layer 206 may comprise a metal oxide (e.g., HfO₂) layerformed to a thickness of between about 10 and about 100 angstroms (Å).

The electrodes 102, 210 and 118 are formed from conductive materialsthat have a desirable work function. In some configurations, theelectrode 102 and 210 are formed from different materials. In someembodiments, the electrodes have a work function that differs by between0.1 and 1 electron volt (eV), or by between 0.4 and 0.6 eV, etc. Forexample, the electrode 102 can be TiN, which has a work function of4.5-4.6 eV, while the electrode 210 can be n-type polysilicon, which hasa work function of approximately 4.1-4.15 eV. Other electrode materials,which can be used in electrode 102, electrode 210 and/or electrode 118include but are not limited to p-type polysilicon (4.9-5.3 eV), n-typepolysilicon, transition metals, transition metal alloys, transitionmetal nitrides, transition metal carbides, tungsten (4.5-4.6 eV),tantalum nitride (4.7-4.8 eV), molybdenum oxide (˜5.1 eV), molybdenumnitride (4.0-5.0 eV), iridium (4.6-5.3 eV), iridium oxide (˜4.2 eV),ruthenium (˜4.7 eV), and ruthenium oxide (˜5.0 eV). Other potentialelectrode materials include a titanium/aluminum alloys (4.1-4.3 eV),nickel (˜5.0 eV), tungsten nitride (˜4.3-5.0 eV), tungsten oxide(5.5-5.7 eV), aluminum (4.2-4.3 eV), copper or silicon-doped aluminum(4.1-4.4 eV), copper (˜4.5 eV), hafnium carbide (4.8-4.9 eV), hafniumnitride (4.7-4.8 eV), niobium nitride (˜4.95 eV), tantalum carbide(approximately 5.1 eV), tantalum silicon nitride (˜4.4 eV), titanium(4.1-4.4 eV), vanadium carbide (˜5.15 eV), vanadium nitride (˜5.15 eV),and zirconium nitride (˜4.6 eV). In one example, the electrode 102 is ametal, metal alloy, metal nitride or metal carbide formed from anelement selected from a group consisting of titanium (Ti), tungsten (W),tantalum (Ta), cobalt (Co), molybdenum (Mo), nickel (Ni), vanadium (V),hafnium (Hf) aluminum (Al), copper (Cu), platinum (Pt), palladium (Pd),iridium (Ir), ruthenium (Ru), and combination thereof. In one example,the electrode 102 comprises a metal alloy selected from the group of atitanium/aluminum alloy (Ti_(x)Al_(y)), or a silicon-doped aluminum(AlSi).

The interface structures disposed between the variable resistance layer206 and one or both of the electrodes are generally configured to adjustthe nonvolatile memory device's performance, such as lowering the formeddevice's switching currents, lowering the required operating voltage,increasing the operation current ratio (I_(ON)/I_(OFF)), reducing thedevice's forming voltage, and reducing the performance variation fromone formed device to another. In general, each of the interface layerstructures formed in a memory element will have at least one of thefollowing regions: a passivation region, an interface coupling region,and a variable resistance layer interface region, which are discussedfurther below.

FIGS. 4A and 5 are schematic side cross-sectional views of a memoryelement 112 found in a switching memory device, such as switching memorydevice 200H or switching memory device 200I, that are in accordance withan embodiment of the present invention. FIG. 4A is a schematic sidecross-sectional view of a memory element 112 found in a switching memorydevice 200H, which contains both a first interface structure 204 and asecond interface structure 208. In one example, as shown in FIG. 4A, thefirst interface structure 204 comprises a passivation region 204A, aninterface coupling region 204B, and a variable resistance layer (VRL)interface region 204C, and the second interface structure 208 comprisesa variable resistance layer interface region 208A, an interface couplingregion 208B, and a passivation region 208C.

FIG. 5 is a schematic side cross-sectional view of a memory element 112found in a switching memory device 2001, which contains both a firstinterface structure 204 and a second interface structure 208, but doesnot require interface coupling regions 204B and/or 208B that are foundin the switching memory device 200H illustrated in FIG. 4A. Therefore,in one configuration of a switching memory device 2001, the firstinterface structure 204 comprises a passivation region 204A and a VRLinterface region 204C, and the second interface structure 208 comprisesa VRL interface region 208A and a passivation region 208C. One will notethat while the discussion and illustrations found in FIGS. 4A and 5,include a memory element 112 that has a first interface structure 204and a second interface structure 208, that this configuration is notintended to be limiting as to the scope of the invention describedherein, since as discussed above in conjunction with FIGS. 3B-3C, amemory element 112 may only require one interface structure disposedtherein.

The passivation regions, such as passivation regions 204A and 208C, areformed at the interface between an electrode, such as the electrode 102or the intermediate electrode 210, and the variable resistance layer206, and are configured to improve the electrical properties at theelectrode interface region. In conventionally formed switching memorydevices, the interface region formed between the electrode and thevariable resistance layer 206 will generally contain many defects thatcan increase carrier recombination and prevent a good electrical contactfrom being created between the formed adjacent layers. In general, theamount of carrier recombination is a function of how many dangling bonds(i.e., unterminated chemical bonds) that are present at the interface.These unterminated chemical bonds act as defect traps, which can act assites for carrier recombination and increase the resistance to the flowof the I_(ON) and I_(OFF) currents through the formed device. Therefore,in one embodiment of the invention, a passivation region 204A and/or apassivation region 208C are formed at the interface between an electrodeand the variable resistance layer 206 to passivate the defects found atthe interface of the electrode. Since the number of defects can varyfrom one formed device to the next, and from one region of the substrateon which the device is formed from another, the variability of thedevice performance can vary from device to device and from one region ofthe substrate to another. Therefore, by forming a passivation layer atthe electrode interface that will reduce the number of interfacialdefects and passivate the interface surface, the device performancevariability across a formed integrated circuit structure (e.g., array offormed devices) can be greatly reduced. Device to device variability isgenerally more of an issue when the formed switching memory devices areconnected in an array, such as shown in FIG. 2C, since the variabilityin the required V_(SET) and V_(RESET) values, and associated variationsin the I_(OFF) and I_(ON) currents, from device to device can affectwhen each of the connected devices reliably switch between the “on” and“off” states. In general, the passivation regions 204A and 208C areformed in such a way that the defect density in these regions are lessthan the defect density at the interface and in the variable resistancelayer 206 to assure that the defects in the formed passivation region(s)do not increase carrier recombination. In one example, a low defectdensity passivation layer is formed by use of an atomic layer deposition(ALD) type of deposition process to control defects and improveswitching and forming voltages in some embodiments.

In some configurations, the material disposed in the passivation regions204A and/or 208C are also selected to adjust the work function of theelectrode material, and thus barrier height (e.g., qφ₁ in FIG. 6A)formed at the interface. In this case, by selecting and formingpassivation regions 204A and/or 208C that desirably alter the workfunction of the electrode material, the magnitude of the required I_(ON)and I_(OFF) currents can be adjusted. FIG. 6A schematically illustratesthe band structure of an interface formed between an electrode and thedielectric variable resistance layer 206 (e.g., labeled “VR layer” inFIG. 6A), in which a first electrode material is disposed adjacent to avariable resistance layer 206 which causes the bands 601 in the variableresistance layer 206 to naturally bend to form a first barrier height(qφ₁). In one configuration of the memory element 112, the formedpassivation region 204A and/or passivation region 208C is used toincrease or decrease the formed barrier height at the interface toadjust the ease with which current will flow through the formedinterface in the formed device when a voltage is applied across theelectrodes. In one configuration, it is desirable to form a passivationregion that alters the work function of the electrode material to causethe bands to bend (see band 602) upwards and cause the barrier height toincrease from qφ₁ to qφ₂. The increased barrier height will thus tend toreduce the magnitude of the I_(ON) and I_(OFF) current that will flowthrough the device during operation, due to the increased energyrequired to move the electrons over and/or tunnel through the barrierand allow the current to flow through the device. One will note that theincrease in barrier height will generally not affect the current ratio(I_(ON)/I_(OFF)), and thus not affect one's ability to detect thedifferent logic states in the switching memory device. In oneembodiment, it may be desirable to further reduce the magnitude of theI_(ON) and I_(OFF) currents by the addition and/or formation of a verythin dielectric layer (e.g., 8-12 Å of oxide) that resides between theformed passivation region 204A, or passivation region 208C, and thevariable resistance layer 206, and acts as a tunnel junction to inhibitelectron flow.

Since the electrode materials disposed in the electrodes 102 and 210 inthe formed memory element 112 may differ, the material used to form thepassivation regions 204A and 208C may also be different. As noted above,in one embodiment, the electrode 102 may comprise a metal, such as atransition metal, transition metal alloy, transition metal carbide,transition metal nitride (e.g., TiN), and the intermediate electrode 210may comprise a heavily doped semiconductor material, such as a heavilydoped silicon material (e.g., n-type polysilicon material). Therefore,the material used to form the passivation regions 204A and 208C may bedifferent, and may be formed by different deposition and/or formationprocesses. In one embodiment, the passivation regions 204A is a metalalloy formed by depositing one or more discrete metal layers and theelectrode material layer (e.g., material in electrode 102) in separateprocessing steps, and then exposing the deposited layers to one or morethermal processing steps to enhance the intermixing and alloying of thetwo or more layers to form a region that has a desirable work functionat the interface of the electrode 102 and the variable resistance layer206. In one example, the passivation regions 204A and 208C comprise anelement selected from a group consisting of titanium (Ti), tungsten (W),tantalum (Ta), cobalt (Co), molybdenum (Mo), nickel (Ni), vanadium (V),hafnium (Hf) aluminum (Al), copper (Cu), platinum (Pt), palladium (Pd),iridium (Ir), ruthenium (Ru), and combination thereof.

In one embodiment, the passivation region 208C is a dielectric layer,such as aluminum oxide (Al_(x)O_(y)), silicon oxide (Si_(x)O_(y)),silicon nitride (Si_(x)N_(y)), silicon oxynitride (Si_(x)O_(y)N_(z)), orzirconium oxide (Zr_(x)O_(y)), which is formed on a heavily dopedpolysilicon type intermediate electrode 210. The dielectric passivationregion 208C may be formed by use of a plasma nitridation, plasmaoxidation, rapid thermal oxidation, chemical vapor deposition (CVD) oratomic layer deposition (ALD) process. In one example, the passivationregion 208C is formed over the surface of the intermediate electrode 210so that the formed layer will passivate the interface of the electrodeand reduce carrier recombination. In one example, the passivationregions 204A and/or 208C comprise a metal or metal oxide materials thatis between about 5 and about 30 angstroms (Å) thick.

The VRL interface regions, such as VRL interface region 204C and 208A,may be formed at the interface between the electrode 102, and/or theintermediate electrode 210, and the variable resistance layer 206, andare configured to improve the electrical properties at the interface ofthe variable resistance layer 206. The VRL interface regions aregenerally used to improve the switching characteristics of the memoryelement 112 by doping portions of the variable resistance layer 206. Inone configuration, the variable resistance layer 206 is doped with amaterial that has an affinity for oxygen (e.g., transition metals (Al,Ti, Zr)) to form a metal-rich variable resistance layer (e.g., HfO_(1.7)vs. HfO₂), which is deficient in oxygen, and thus has a larger number ofoxygen vacancy type defects. The additional vacancy defects can reducethe required switching and forming voltages, reduce the device operatingcurrent(s), and reduce the device to device variation in a formed memoryelement. One will note that a forming voltage is generally applied tothe memory element 112 to “burn-in” and configure the variableresistance layer 206 material, so that a more repeatable deviceperformance is achieved throughout memory element's life.

In one embodiment, the VRL interface regions 204C and 208A are formedusing a material that has a higher Gibbs energy (AG) than materialcontained in the variable resistance layer 206. The higher Gibbs energymaterial, used to help form the VRL layer(s), will thus tend to diffuseinto, intermix with and/or form an alloy with portions of the materialin the variable resistance layer 206 to form the VRL interface regions204C and/or 208A during the one or more thermal processing steps used toform the switching memory device. Also, the VRL interface region 204Cand/or a VRL interface region 208A may be formed at the interfacebetween an electrode and the variable resistance layer 206 to reduce thedefect contained on the variable resistance layer 206 side of theinterface, and thus improve the electrical properties of the formedinterface. In one example, the VRL interface regions 204C and 208Acomprises the material from which the variable resistance layer 206 isformed (e.g., HfO_(x)) with a dopant atom selected from a groupconsisting of aluminum, zirconium, titanium, tungsten, tantalum, cobalt,molybdenum, nickel, vanadium, copper, platinum, palladium, iridium,hafnium, and ruthenium disposed therein. In one example, the VRLinterface regions 204C and/or 208A are between about 5 and about 30angstroms (Å) thick. In one configuration, the dopant atom comprises anelement that is different than the element from which the electrodes aresubstantially formed.

Also, in some configurations of the memory element 112, the firstinterface structure 204 or second interface structure 208, such as thepassivation regions 204A, 208C, interface coupling regions 204B, 208B orVRL interface regions 204C, 208A, have a desirable thickness so thatthey will act as a diffusion barrier that prevents the diffusion of thematerial found in the electrodes 102, 210, and 118 from diffusing intothe variable resistance layer 206, or vice versa, during a thermalprocessing step used to form the memory element 112. Moreover, it isoften desirable for the materials in the first interface structure 204or second interface structure 208 to preferentially diffuse into and/orat least partially intermix with the material in the electrodes and thevariable resistance layer.

In one embodiment, as shown in FIG. 4A, the memory element 112 comprisesone or more interface coupling regions, such as interface couplingregions 204B and 208B, which are formed between an electrode (e.g.,electrode 102 or intermediate electrode 210) and the variable resistancelayer 206. The interface coupling region(s) are configured to improvethe electrical properties of a formed switching memory device bylowering the current that will flow through the device, while notaffecting the current ratio (I_(ON)/I_(OFF)), and thus ability to detectthe different logic states in the switching memory device. An interfacecoupling region is formed from a material that has a desirable band gapand thickness so that when it is disposed between the electrode and thevariable resistance layer 206 it will tend to block or inhibit currentflow through the memory element 112. FIG. 6B schematically illustratesthe band structure of an interface formed between an electrode and thedielectric variable resistance layer 206 (e.g., labeled “VR layer” inFIG. 6B), in which an interface coupling region is disposed between anelectrode and a variable resistance layer 206, which forms a blockingregion 608 that inhibits the flow of current in either direction throughthe formed interface due to the presence of the interface couplingregion. In one embodiment, the material disposed in the interfacecoupling region has a band gap that is larger than the material found inthe variable resistance layer 206. In one configuration, the variableresistance layer 206 is a hafnium oxide (Hf_(x)O_(y)) material and theinterface coupling region is formed from a material selected from agroup of zirconium oxide (Zr_(x)O_(y)), tantalum oxide (Ta_(x)O_(y)),aluminum oxide (Al_(x)O_(y)), yttrium oxide (Y_(x)O_(y)), dysprosiumoxide (Dy_(x)O_(y)), and ytterbium oxide (Yb_(x)O_(y)). The presence ofthe interface coupling region will naturally form a barrier height (qφ₃)at the interface between the electrode and the interface couplingregion. The size of the barrier height (qφ₃) is strongly dependent onthe band gap of the material used to form the interface coupling regionand the material from which the electrode is formed. One will note thatin some cases it is desirable to form a passivation region (e.g., region204A) between the electrode (e.g., electrode 102) and the interfacecoupling layer (e.g., region 204B) to further modify and adjust theformed barrier height formed at the interface, such as varying thebarrier height from qφ₃ to qφ₄. The adjusted barrier height will thustend to adjust the magnitude of the I_(ON) and I_(OFF) current that canflow through the device during operation, while not affecting thecurrent ratio (I_(ON)/I_(OFF)), and thus one's ability to detect thedifferent logic states in the switching memory device.

In one configuration of the memory element 112, an interface couplingregion 204B and/or an interface coupling region 208B are formed so thatit has a desirable thickness to help further adjust the ease with whichcurrent can flow through the formed interface in the formed device. Byadjusting the thickness of the interface coupling region, the currentflow through the memory element can be adjusted, since a sufficientlythin interface coupling region can allow tunneling currents to become animportant factor in the amount of current that flows through the formedinterface coupling region and memory element 112. In one embodiment, aninterface coupling region formed from one of the materials discussedabove has a thickness less than about 30 angstroms (Å), such as betweenabout 5 and about 30 Å.

FIG. 6C schematically illustrates the band structure of the memoryelement 112, which is similar to the switching memory device 200Hillustrated in FIG. 4A, that has a first interface structure 204 and thesecond interface structure 208 that are disposed between the variableresistance layer 206 and their respective electrodes. In one embodiment,the first and second interface structures 204 and 208 each comprise amaterial that has a band gap larger than the variable resistance layer206 material, and thus both tend to reduce the magnitude of the I_(ON)and I_(OFF) current that can flow through the device during operation,while not affecting the current ratio (I_(ON)/I_(OFF)), and thus one'sability to detect the different logic states in the switching memorydevice. In one example, as illustrated in FIG. 6C, the first interfacestructure 204 comprises one or more layers of a dielectric material thathas a band structure 614, the variable resistance layer 206 comprises adielectric material that has a band structure 616, and the secondinterface structure 208 comprises one or more layers of a dielectricmaterial that has a band structure 618.

FIGS. 4B and 4C are schematic cross-sectional views of a memory elementthat illustrate different stages of a memory element formation processin which the first interface structure 204 and the second interfacestructure 208 are formed. FIG. 7 is a schematic depiction of a processsequence 700 that may be used to form the switching memory device 200Hillustrated in FIGS. 4A and 4C, according to one embodiment of theinvention. FIG. 4B illustrates an intermediate stage of forming aswitching memory device, or switching memory device 200G, that containsa series of stacked discrete layers including an electrode 102,interface layer 201, interface layer 203, interface layer 205, variableresistance layer 206, interface layer 207, interface layer 209,interface layer 211 and intermediate electrode 210 that are formed oneon top of each other by use of the processing sequence, such asprocessing sequence 700 discussed below. FIG. 4C illustrates the finalformed switching memory device 200H that contains the formed electrode102, first interface structure 204, variable resistance layer 206,second interface structure 208, and intermediate electrode 210, whichare formed by performing one or more subsequent processing steps, suchas one or more thermal processing steps. The subsequent processing stepsare often used to heat treat or activate dopants in one or more of thelayers disposed in the formed device (e.g., current steering elements)or other devices formed on the chip.

Referring to FIGS. 4B and 7, at step 702 an intermediate electrode 210is formed over a substrate or provided for further processing. In oneembodiment, the intermediate electrode 210 is a highly doped polysiliconlayer that is formed using a conventional CVD or ALD type polysilicondeposition technique. In some cases, an optional native oxide layerremoval step may be performed after forming the intermediate electrodelayer 210 by use of a wet chemical processing technique, or conventionaldry clean process that is performed in a plasma processing chamber. Itshould be noted that although only the intermediate electrode 210 isdepicted in FIG. 4B, the intermediate electrode 210 may be provided on asubstrate (i.e., substrate 201 shown in FIG. 3A) that may have thesteering device 216 and the electrode 218 formed thereon as well.Alternatively, in the case where no steering device 216 is provided, thedepicted intermediate electrode 210 is the electrode 218. In oneexample, the intermediate electrode 210 comprises polysilicon and isbetween about 50 and about 5000 angstroms (Å) thick.

At step 704, as depicted in FIG. 4B and 7, an interface layer 211 isformed on the intermediate electrode 210 using a deposition process,such as a PVD, CVD (e.g., LPCVD, PECVD), ALD (e.g., PEALD) or othersimilar process. In one embodiment, the interface layer 211 is a metaloxide layer (e.g., Al₂O₃, ZrO₂) that is formed by use of a CVD or ALDprocess in which a metal precursor and an oxygen containing gas isprovided over the surface of the substrate. In one example, theinterface layer 211 may be formed to a thickness between about 3 andabout 10 angstroms (Å), and comprise a material such as Al₂O₃ or ZrO₂.In another embodiment of step 704, the interface layer 211 is formed onthe intermediate electrode 210 by performing a nitridation and/oroxidation process to form a SiON interface layer on a polysilicon typeintermediate electrode 210. In one example of a nitridation and/oroxidation process, the interface layer 211 is annealed and/or exposed toan RF plasma in a nitrogen environment, such as NH₃, N₂O, NO, or thelike. In one example, the partially formed device 200 is heated to atemperature between about 600 and about 800° C. at a pressure of lessthan about 100 Torr for a time period between about 1 second and about120 seconds to form a SiON interface layer 211.

At step 706, as depicted in FIG. 4B and 7, a first optional interfacelayer 209 is formed over the interface layer 211 using a depositionprocess, such as a PVD, CVD, ALD or other similar process. In oneembodiment, the interface layer 209 is a metal oxide layer (e.g., Al₂O₃,ZrO₂) or metal layer (e.g., Al, Ti, Zr, Ni) that is formed by use of aPVD, CVD or ALD process. In one configuration, the first optionalinterface layer comprises a material that is different, or has differentmaterial properties, from the interface layer 211. The first optionalinterface layer 209 may be used to form at least part of a passivationregion, an interface coupling region and/or a VRL interface region in aformed switching memory device. In one example, an ALD process usingtetrakis(dimethylamino)zirconium (TDMAZ) and an oxygen containingprecursor (e.g., ozone, room temperature water (H₂O)) at a temperatureof about 200-300° C. is used to form an 8 Angstrom (Å) thick zirconiumoxide (ZrO_(x)) containing interface layer 211. In one example, a PVDprocess is used to deposit an aluminum (Al) layer that is then treatedwith ozone (O₃) at a temperature of about 100-300° C. to form a 20 Åthick aluminum oxide (Al_(x)O_(y)) containing interface layer 211. Inone example, an ALD process using trimethylaluminium (TMA) and an oxygencontaining precursor at a temperature of about 200-300° C. to form an 8Å thick aluminum oxide (Al_(x)O_(y)) containing interface layer 211.

At step 708, as depicted in FIG. 4B and 7, a second optional interfacelayer 207 is formed over the first optional interface layer 209 using adeposition process, such as a PVD, CVD, ALD or other similar process. Inone embodiment, the interface layer 207 is a metal oxide layer (e.g.,Al₂O₃, ZrO₂) or metal layer (e.g., Al, Ti, Zr, Ni) that is formed by useof a PVD, CVD or ALD process. In one example, the interface layer 207may be formed to a thickness between about 3 and about 10 angstroms, andcomprise a material such as Al, Ti, Ni or Zr. In one configuration, thesecond optional interface layer comprises a material that is differentfrom the first optional interface layer 209. One will note that, in someconfigurations, it may be desirable to form one or more additionalinterface layers that each comprise different materials, or havedifferent material properties, over the interface layer 207 to helptailor the electrical and mechanical characteristics of the interfacestructure that is to be formed in the switching memory device. In thisconfiguration, step 708 may be performed multiple times to form adesirable number of layers that each comprise different materials, orhave different material properties. The second optional interface layer207 may be used to form at least part of an interface coupling regionand/or a VRL interface region in a formed switching memory device. Inone example, an ALD process using TMA and an oxygen containing precursorat a temperature of about 200-300° C. is used to form an 8 Å thickaluminum oxide (Al_(x)O_(y)) containing interface layer 209.

Referring to FIGS. 4B and 7, at step 710, the variable resistance layer206 is deposited on the interface layer 208 using a deposition process.The variable resistance layer 206 may comprise a metal oxide layer, suchas Hf_(x)O_(y), Ta_(x)O_(y), Al_(x)O_(y), La_(x)O_(y), Y_(x)O_(y),Dy_(x)O_(y), Yb_(x)O_(y) and/or Zr_(x)O_(y), formed to a thickness ofbetween about 20 and about 100 angstroms (Å), such as between about 30and about 50 angstroms (Å). The variable resistance layer 206 can bedeposited using any desired technique, but in some embodiments describedherein is deposited using an ALD process. In other embodiments, thevariable resistance layer 206 can be deposited using a CVD (e.g., LPCVD,PECVD) or ALD (e.g., PEALD), physical vapor deposition (PVD), liquiddeposition processes, and epitaxy processes. It is believed that PEALDprocesses can be used to control defects and improve switching andforming voltages in some embodiments. In one example, an ALD processusing tetrakis(dimethylamino)hafnium (TDMAH) and an oxygen containingprecursor at a temperature of about 250° C. is used to form an 50 Åthick hafnium oxide (Hf_(x)O_(y)) containing variable resistance layer206.

At step 712, as depicted in FIG. 4B and 7, an interface layer 205 isformed over the variable resistance layer 206 using a depositionprocess, such as a PVD, CVD, ALD or other similar process. In oneembodiment, the interface layer 205 is a metal oxide layer (e.g., Al₂O₃,ZrO₂) or metal layer (e.g., Al, Ti, Zr, Ni) that is formed by use of aPVD, CVD or ALD process. In one example, an ALD process using TMA and anoxygen containing precursor at a temperature of about 200-300° C. isused to form an 8 Å thick aluminum oxide (Al_(x)O_(y)) containinginterface layer 206. In one example, the interface layer 203 may beformed to a thickness between about 3 and about 10 angstroms, andcomprise a material such as Al, Ti, Ni or Zr. The interface layer 205may be used to form at least part of a VRL interface region, aninterface coupling region and/or a passivation region in a formedswitching memory device.

At step 714, as depicted in FIG. 4B and 7, a third optional interfacelayer 203 is formed over the interface layer 205 using a depositionprocess, such as a PVD, CVD, ALD or other similar process. In oneembodiment, the interface layer 203 is a metal oxide layer (e.g., Al₂O₃,ZrO₂) or metal layer (e.g., Al, Ti, Zr, Ni) that is formed by use of aPVD, CVD or ALD process. In one configuration, the third optionalinterface layer 203 comprises a material that is different, or havedifferent material properties, from the interface layer 205. The thirdoptional interface layer 203 may be used to form at least part of a VRLinterface region, an interface coupling region and/or a passivationregion in a formed switching memory device. In one example, a PVDprocess is used to deposit an aluminum (Al) layer at a temperature ofabout 100-300 ° C. to form a 20 Å thick aluminum (Al) interface layer203.

At step 716, as depicted in FIG. 4B and 7, a fourth optional interfacelayer 201 is formed over the third interface layer 203 using adeposition process, such as a PVD, CVD, ALD or other similar process. Inone embodiment, the fourth optional interface layer 201 is a metal oxidelayer (e.g., Al₂O₃, ZrO₂) or metal layer (e.g., Al, Ti, Zr, Ni) that isformed by use of a PVD, CVD or ALD process. In one configuration, thefourth optional interface layer 201 comprises a material that isdifferent from the third interface layer 203. One will note that, insome configurations, it may be desirable to form one or more additionalinterface layers that each comprise different materials, or havedifferent material properties, over the fourth interface layer 201 tohelp tailor the electrical and mechanical characteristics of theinterface structure that is to be formed in the switching memory device.In this configuration, step 716 may be performed multiple times to forma desirable number of layers that each comprise different materials, orhave material properties. In one example, the fourth interface layer maycomprise a material selected from a group consisting of aluminum,titanium, tungsten, tantalum, cobalt, molybdenum, nickel, vanadium,copper, platinum, palladium, iridium, and ruthenium. In another example,the fourth interface layer may comprise a material selected from a groupconsisting of tantalum, aluminum, lanthanum, yttrium, dysprosium,ytterbium and zirconium. The interface layer 201 may be used to form atleast part of an interface coupling region and/or a passivation regionin a formed switching memory device.

At step 718, the electrode 102 is formed on the interface layer 201 asshown in FIG. 4B and using one or more of the materials that arediscussed above. The electrode 102 layer may be deposited using adeposition process, such as a PVD, CVD, ALD or other similar process. Inone example, the electrode layer 102 is between about 500 Å and 1 μmthick.

At step 720, the formed switching memory device 200G is annealed at atemperature of greater than about 550° C. In one example, the formedswitching memory device 200G is annealed at a temperature of greaterthan about 700° C. In another example, the formed switching memorydevice 200G is annealed at a temperature of between about 550° C. andabout 1000° C. for a period of time between about 30 seconds and about20 minutes. In one example, the device is annealed using ahydrogen/argon mixture (e.g., 2-10% hydrogen, 90-98% argon), althoughother anneals such as vacuum anneals, oxidizing anneals, etc. can beused. In one example, the annealing process is performed at atemperature of about 750° C. for about 1 minute in a forming gasenvironment maintained at a pressure of about 760 Torr. In anotherexample of an annealing process, the formed device is heated to atemperature of about 750° C. for about 1 minute in an oxygen richforming gas environment, wherein the processing environment comprisesbetween about 0.5 and 10% of oxygen, between about 2 and 6% of hydrogen,between about 10 and 97.5% of nitrogen, and optionally the remainingpercentage being a carrier gas (e.g., argon), and the environment ismaintained at a pressure of between about 0.5 and 100 Torr. Theprocess(es) performed at step 720, are generally configured to cause thelayers disposed in the switching memory device 200G (FIG. 4B) to formthe various regions (e.g., regions 204A, 204B, and/or 204C) in the firstinterface layer 204 and the various regions (e.g., regions 208A, 208Band/or 208C) in the second interface layer 208, as well as activate andor desirably process the other layers formed in the switching memorydevice.

In some embodiments of the invention, multiple thermal processing steps,such as described in step 720, are performed during the processingsequence 700, rather than performing just one thermal process (step 720)at the end of the processing sequence. In one example, a thermal processmay be performed during or after each step, during or after every otherstep or in any other sequence that is desirable to form the switchingmemory device 200H. In some embodiments of the invention, the thermalprocessing steps are performed during part of the one or more depositionprocess steps found in the processing sequence 700, rather than justperforming one thermal process at the end of the processing sequence.

Process and Device Examples

In one example of a process of forming a switching memory device, afterperforming the steps 702-718 in the processing sequence 700, a memoryelement 112 is formed that comprises: an intermediate electrode 210comprising an n-doped polysilicon layer, an interface layer 211 that isbetween about 8 Å-20 Å thick and comprises aluminum oxide (Al₂O₃), aninterface layer 209 that is about 50 Å thick and comprises zirconiumoxide (ZrO_(x)), an interface layer 207 that is about 50 Å thick andcomprises aluminum (Al), a variable resistance layer 206 that is about50 Å thick and comprises hafnium oxide (HfO_(x)), an interface layer 205that is between about 8 Å-20 Å thick and comprises aluminum oxide(Al₂O₃), an interface layer 203 that is about 50 Å thick and compriseszirconium oxide (ZrO_(x)), an interface layer 201 that is about 50 Åthick and comprises aluminum (Al), and an electrode 102 that comprises alayer of titanium nitride (TiN). After forming the switching memorydevice 200G (FIG. 4B), then at least one thermal processing step isperformed, such as step 720, to form switching memory device 200H (FIG.4C) comprises: an intermediate electrode 210 comprising an n-dopedpolysilicon layer, a passivation region 208C that is between about 8Å-20 Å thick and comprises aluminum oxide (Al₂O₃), an interface couplingregion 208B that is about 50 Å thick and comprises zirconium oxide(ZrO_(x)), a VRL interface region 208A that is about 5 Å thick andcomprises hafnium aluminum oxide (Hf_(x)Al_(y)O_(z)), a variableresistance layer 206 that is about 30 Å thick and comprises hafniumoxide (HfO_(x)), a VRL interface region 204C that is about 5 Å thick andcomprises hafnium aluminum oxide (Hf_(x)Al_(y)O_(z)), an interfacecoupling region 204B that is about 50 Å thick and comprises zirconiumoxide (ZrO_(x)), a passivation region 204A that is between about 5 Åthick and comprises titanium aluminum nitride (Ti_(x)Al_(y)N_(z)), andan electrode 102 that comprises a titanium nitride (TiN) layer.

In another exemplary process of forming the switching memory device,after performing the steps 702-706, 710-714 and 718, a memory element112 is formed that comprises: an intermediate electrode 210 comprisingan n-doped polysilicon layer, an interface layer 211 that is betweenabout 8 Å-20 521 thick and comprises aluminum oxide (Al₂O₃), aninterface layer 209 that is about 50 Å thick and comprises aluminum(Al), a variable resistance layer 206 that is about 50 Å thick andcomprises hafnium oxide (HfO_(x)), an interface layer 205 that isbetween about 8 Å-20 Å thick and comprises aluminum oxide (Al₂O₃), aninterface layer 203 that is about 50 Å thick and comprises aluminum(Al), and an electrode 102 that comprises a layer of titanium nitride(TiN). Next, after performing at least one thermal processing step, suchas step 720, the formed switching memory device will generally comprise:an intermediate electrode 210 comprising an n-doped polysilicon layer, apassivation region 208C that is between about 8 Å-20 Å thick andcomprises aluminum oxide (Al₂O₃), a VRL interface region 208A that isabout 8 Å thick and comprises hafnium aluminum oxide(Hf_(x)Al_(y)O_(z)), a variable resistance layer 206 that is about 30 Åthick and comprises hafnium oxide (HfO_(x)), a VRL interface region 204Cthat is about 8 Å thick and comprises hafnium aluminum oxide(Hf_(x)Al_(y)O_(z)), a passivation region 204A that is about 10 Å thickand comprises titanium aluminum nitride (Ti_(x)Al_(y)N_(z)), and anelectrode 102 that comprises a titanium nitride (TiN) layer.

In yet another exemplary process of forming the switching memory device,after performing the steps 702, 710-714 and 718, a memory element 112 isformed that comprises: an intermediate electrode 210 comprising ann-doped polysilicon layer, a variable resistance layer 206 that is about50 Å thick and comprises hafnium oxide (HfO_(x)), an interface layer 205that is between about 8 Å-20 Å thick and comprises aluminum oxide(Al₂O₃), an interface layer 203 that is about 50 Å thick and comprisesaluminum (Al), and an electrode 102 that comprises a layer of titaniumnitride (TiN). Next, after performing at least one thermal processingstep, such as step 720, the formed switching memory device willgenerally comprise: an intermediate electrode 210 comprising an n-dopedpolysilicon layer, a variable resistance layer 206 that is about 50 Åthick and comprises hafnium oxide (HfO_(x)), a VRL interface region 204Cthat is about 20 Å thick and comprises hafnium aluminum oxide(Hf_(x)Al_(y)O_(z)), a passivation region 204A that is about 10 Å thickand comprises titanium aluminum nitride (Ti_(x)Al_(y)N_(z)), and anelectrode 102 that comprises titanium nitride (TiN) layer.

In yet another exemplary process of forming the switching memory device,after performing the steps 702-706, 710 and 718, a memory element 112 isformed that comprises: an intermediate electrode 210 comprising ann-doped polysilicon layer, an interface layer 211 that is between about8 Å-20 Å thick and comprises aluminum oxide (Al₂O₃), an interface layer209 that is about 50 Å thick and comprises aluminum (Al), a variableresistance layer 206 that is about 50 Å thick and comprises hafniumoxide (HfO_(x)), and an electrode 102 that comprises a layer of titaniumnitride (TiN). Next, after performing at least one thermal processingstep, such as step 720, the formed switching memory device willgenerally comprise: an intermediate electrode 210 comprising an n-dopedpolysilicon layer, a passivation region 208C that is between about 8Å-20 Å thick and comprises aluminum oxide (Al₂O₃), a VRL interfaceregion 208A that is about 10 Å thick and comprises hafnium aluminumoxide (Hf_(x)Al_(y)O_(z)), a variable resistance layer 206 that is about30 Å thick and comprises hafnium oxide (HfO_(x)), and an electrode 102that comprises a titanium nitride (TiN) layer.

In yet another exemplary process of forming the switching memory device,after performing the steps 702-706, 710 and 718, a memory element 112 isformed that comprises: an intermediate electrode 210 comprising ann-doped polysilicon layer, an interface layer 211 that is between about8 Å-20 Å thick and comprises silicon dioxide (SiO₂), an interface layer209 that is about 8 Å-20 Å thick and comprises aluminum oxide (Al₂O₃), avariable resistance layer 206 that is about 50 Å thick and compriseshafnium oxide (HfO_(x)), and an electrode 102 that comprises titaniumnitride (TiN). Next, after performing at least one thermal processingstep, such as step 720, the formed switching memory device willgenerally comprise: an intermediate electrode 210 comprising an n-dopedpolysilicon layer, a passivation region 208C that is between about 8Å-20 Å thick and comprises silicon dioxide (SiO₂), an interface couplingregion 208B that is about 8 Å-20 Å thick and comprises aluminum oxide(Al₂O₃), a VRL interface region 208A that is about 10 Å thick andcomprises hafnium aluminum oxide (Hf_(x)Al_(y)O_(z)), a variableresistance layer 206 that is about 30 Å thick and comprises hafniumoxide (HfO_(x)), and an electrode 102 that comprises a titanium nitride(TiN).

In yet another exemplary process of forming the switching memory device,after performing the steps 702 and 710-718, a memory element 112 isformed that comprises: an intermediate electrode 210 comprising ann-doped polysilicon layer, a variable resistance layer 206 that is about50 Å thick and comprises hafnium oxide (HfO_(x)), an interface layer 205that is between about 8 Å-20 Å thick and comprises aluminum oxide(Al₂O₃), an interface layer 203 that is between about 8 Å-20 Å thick andcomprises zirconium oxide (ZrO _(x)), an interface layer 201 that isabout 50 Å thick and comprises aluminum (Al), and an electrode 102 thatcomprises titanium nitride (TiN). Next, after performing at least onethermal processing step, such as step 720, the formed switching memorydevice will generally comprise: an intermediate electrode 210 comprisingan n-doped polysilicon layer, a variable resistance layer 206 that isabout 30 Å thick and comprises hafnium oxide (HfO_(x)), a VRL interfaceregion 204C that is about 15 Å thick and comprises hafnium aluminumoxide (Hf_(x)Al_(y)O_(z)), an interface coupling region 204B that isabout 8 Å-20 Å thick and comprises zirconium oxide (ZrO_(x)), apassivation region 204A that is between about 15 Å thick and comprisestitanium aluminum nitride (Ti_(x)Al_(y)N_(z)), and an electrode 102 thatcomprises a titanium nitride (TiN) layer.

In yet another exemplary process of forming the switching memory device,after performing the steps 702 and 710-718, a memory element 112 isformed that comprises: an intermediate electrode 210 comprising ann-doped polysilicon layer, a variable resistance layer 206 that is about50 Å thick and comprises hafnium oxide (HfO_(x)), an interface layer 205that is between about 8 Å-20 Å thick and comprises aluminum oxide(Al₂O₃), and an electrode 102 that comprises titanium nitride (TiN).Next, after performing at least one thermal processing step, such asstep 720, the formed switching memory device will generally comprise: anintermediate electrode 210 comprising an n-doped polysilicon layer, avariable resistance layer 206 that is about 50 Å thick and compriseshafnium oxide (HfO_(x)), a VRL interface region 204C that is about 15 Åthick and comprises hafnium aluminum oxide (Hf_(x)Al_(y)O_(z)), aninterface coupling region 204B that is about 8 Å-20 Å thick andcomprises aluminum oxide (Al₂O₃), a passivation region 204A that isbetween about 15 Å thick and comprises titanium aluminum nitride(Ti_(x)Al_(y)N_(z)), and an electrode 102 that comprises a titaniumnitride (TiN) layer.

The foregoing is merely illustrative of the principles of this inventionand various modifications can be made by those skilled in the artwithout departing from the scope and spirit of the invention as definedby the claims that follow.

1. A method of forming a nonvolatile memory element, comprising: forminga first electrode layer comprising a first electrode material over asurface of a substrate; forming a first interface layer comprising afirst interface material in contact with the first electrode layer;forming a second interface layer comprising a second interface material;forming a variable resistance layer comprising a variable resistancematerial in contact with the second interface layer; and heating thesubstrate; wherein the material in the first interface region has a workfunction greater than a work function of the first electrode material;wherein the second interface layer is disposed between the firstinterface layer and the variable resistance layer; wherein heating thesubstrate forms a first interface region that comprises the firstinterface material and the first electrode material; and wherein heatingthe substrate forms a second interface region that comprises the secondinterface material and the variable resistance material.
 2. The methodof claim 1, wherein the first electrode material comprises titanium, andthe first interface material comprises at least one of aluminum,titanium, zirconium or nickel.
 3. The method of claim 1, wherein thefirst electrode layer comprises silicon.
 4. The method of claim 3,further comprising removing a native oxide after forming the firstelectrode layer.
 5. The method of claim 3, wherein the first interfacelayer comprises at least one of aluminum oxide, silicon oxide, siliconnitride, silicon oxynitride and zirconium oxide.
 6. The method of claim3, wherein the first interface layer is formed by nitridation oroxidation of the first electrode layer.
 7. The method of claim 3,wherein the first interface layer is formed by annealing or RF plasmaexposure in a nitrogen environment.
 8. The method of claim 1, whereinthe first interface layer or the second interface layer is formed bychemical vapor deposition or atomic layer deposition using a metalprecursor and an oxygen containing gas.
 9. The method of claim 1,wherein the variable resistance layer is formed by at least one ofchemical vapor deposition, physical vapor deposition, atomic layerdeposition, or plasma-enhanced atomic layer deposition, liquiddeposition, or epitaxy.
 10. The method of claim 1, further comprising:forming a second electrode layer comprising a second electrode material;and forming a current steering device, wherein the second electrode isdisposed between the current steering device and the variable resistancelayer.
 11. The method of claim 1, further comprising: forming a thirdinterface layer comprising a third interface material, wherein the thirdinterface layer is in contact with the variable resistance layer;forming a fourth interface layer comprising a fourth interface material;and forming a second electrode layer comprising a second electrodematerial; wherein the fourth interface layer is in contact with thesecond electrode layer and is disposed between the second electrodelayer and the third interface layer; and wherein heating the substrateforms a third interface region that comprises the third interfacematerial and the variable resistance material.
 12. The method of claim11, wherein the fourth interface material comprises oxygen and at leastone of tantalum, aluminum, lanthanum, yttrium, dysprosium, ytterbium andzirconium.
 13. The method of claim 11, wherein the fourth interfacematerial comprises oxygen and at least one of aluminum, titanium,tungsten, tantalum, cobalt, molybdenum, nickel, vanadium, copper,platinum, palladium, iridium, and ruthenium.
 14. The method of claim 1,wherein: the variable resistance material comprises oxygen and at leastone of hafnium, tantalum, aluminum, lanthanum, yttrium, dysprosium,ytterbium or zirconium and the second interface material comprises atleast one of aluminum, titanium, tungsten, tantalum, cobalt, molybdenum,nickel, vanadium, copper, platinum, palladium, iridium or ruthenium. 15.The method of claim 1, wherein: the first electrode material comprisesat least one of titanium, aluminum, tungsten, tantalum, cobalt,molybdenum, nickel, vanadium, copper, platinum, palladium, iridium orruthenium; the variable resistance layer comprises at least one ofhafnium oxide, tantalum oxide, aluminum oxide, lanthanum oxide, yttriumoxide, dysprosium oxide, ytterbium oxide or zirconium oxide; and thefirst interface material comprises at least one of titanium, aluminum,tungsten, tantalum, cobalt, molybdenum, nickel, vanadium, copper,platinum, palladium, iridium, or ruthenium, wherein the first interfacematerial and the first electrode material are different materials. 16.The method of claim 1, wherein the variable resistance layer comprisesat least one of hafnium oxide, tantalum oxide, aluminum oxide, lanthanumoxide, yttrium oxide, dysprosium oxide, ytterbium oxide or zirconiumoxide.
 17. The method of claim 1, wherein heating the substrate furthercomprises exposing a surface of the substrate to an environmentcomprising between about 0.5 and about 10% oxygen, between about 2 andabout 6% hydrogen, and between about 10 and about 97.5% nitrogen. 18.The method of claim 1, wherein heating the substrate further comprisesexposing a surface of the substrate to an environment comprising betweenabout 2% and 10% hydrogen and between about 90% and 98% argon.
 19. Themethod of claim 17, wherein heating the substrate further comprisesheating the substrate to a temperature between about 550° C. and about1000° C. for a period of time between about 30 seconds and about 20minutes.
 20. The method of claim 1, wherein the Gibbs energy of thefirst interface material is greater than the Gibbs energy of thevariable resistance material.